Men who dream of starting a family may want to pass on the ibuprofen the next time they have a headache. A new study says the well-known painkiller could cause fertility issues in males.

The study, published this week in the journal Proceedings of the National Academy of Sciences (PNAS), monitored 31 healthy white men aged 18 to 35. The volunteers were interviewed, completed a questionnaire assessing their physical activity, and gave a blood sample. The men were then divided into two groups, 14 in an ibuprofen group and 17 in a placebo group.